filters

type Filter interface {
	// Name identifies the filter in diagnostics; it is also the shape of
	// the savings-ledger key for commands this filter claims.
	Name() string
	// Match reports whether this filter handles the command whose parsed
	// fields these are — env assignments already stripped, fields[0] the
	// program (path base not yet stripped; use the progOf helper).
	Match(fields []string) bool
	// Filter rewrites raw (ANSI already stripped) into compact form. exit
	// is the process exit code and steers verbosity: 0 may collapse hard to
	// a summary; nonzero must preserve failure detail; an unmodeled nonzero
	// should return raw untouched so a real failure is never hidden.
	Filter(fields []string, raw string, exit int) string
}

type GitFilter struct{}

type GoFilter struct{}

type InstallFilter struct{}

type OutputMatch struct {
	Pattern *regexp.Regexp
	Message string
}

type PytestFilter struct{}

type Replacement struct {
	Pattern *regexp.Regexp
	Repl    string
}

type Rule struct {
	// Name is the diagnostics / ledger-key label.
	Name string
	// Command matches the normalized command (program base + args joined by
	// single spaces, env assignments stripped), e.g. `^make\b`.
	Command *regexp.Regexp
	// Strip drops any line matching one of these.
	Strip []*regexp.Regexp
	// Keep, when non-empty, keeps only lines matching one of these (applied
	// after Strip).
	Keep []*regexp.Regexp
	// Replace applies regex substitutions before line filtering.
	Replace []Replacement
	// PassFail turns the command into a binary result: on success (exit 0)
	// the whole output collapses to a single "ok" line (OnEmpty if set, else
	// "<name>: ok") regardless of content; on failure it falls through to the
	// normal strip/keep pipeline (or raw, with KeepOnError) so the error is
	// still shown. For commands whose successful output is pure noise
	// (builds, formatters) and only the exit code matters.
	PassFail bool
	// Summarize collapses the whole output to Message when Pattern matches
	// AND the command succeeded (exit 0). This is the success-detection
	// short-circuit ("BUILD SUCCESSFUL" → "gradle: ok"); it never fires on a
	// failing run, so an error is never replaced by a rosy summary.
	Summarize []OutputMatch
	// MaxLines keeps the first N lines (0 = unbounded); TailLines keeps the
	// last N. Prefer leaving these zero on build/test commands so a late
	// error is never truncated — the universal cap still bounds runaways.
	MaxLines  int
	TailLines int
	// TruncateAt caps each line's length in bytes (0 = unbounded).
	TruncateAt int
	// OnEmpty is emitted when filtering removed everything ("make: ok").
	OnEmpty string
	// KeepOnError returns the raw output verbatim on a nonzero exit.
	KeepOnError bool
}